Csi definitions and feedback modes for coordinated multi-point transmission

ABSTRACT

A method and apparatus report channel state information (CSI) feedback of a user equipment (UE) in a coordinated multipoint communication system. The method includes identifying, when downlink transmissions to the UE are configured with at least two CSI subframe subsets, an interference measurement resource within one of the CSI subframe subsets belonging to a CSI reference resource. The method also includes using the identified interference measurement resource to derive an interference measurement. The apparatus includes a controller configured to, when downlink transmissions to the UE are configured with at least two CSI subframe subsets, identify an interference measurement resource within one of the CSI subframe subsets belonging to a CSI reference resource. The controller is configured to use the identified interference measurement resource to derive an interference measurement.

CROSS-REFERENCE TO RELATED APPLICATION(S) AND CLAIM OF PRIORITY

The present application claims priority to U.S. Provisional PatentApplication Ser. No. 61/644,957 filed May 9, 2012, entitled “CSIDEFINITIONS AND FEEDBACK MODES FOR COORDINATED MULTI-POINTTRANSMISSION”. The content of the above-identified patent document isincorporated herein by reference.

TECHNICAL FIELD

The present application relates generally to Coordinated Multi-Point(CoMP) communication and, more specifically, to channel stateinformation (CSI) feedback for CoMP communication.

BACKGROUND

CoMP technology has been standardized to allow the user equipment (UE)to receive signals from multiple transmission points (TPs) in differentusage scenarios. The different scenarios include: 1) a homogeneousnetwork with intra-site CoMP, 2) a homogeneous network with hightransmit (Tx) power remote radio heads (RRHs), 3) a heterogeneousnetwork with low-power RRHs within the macro cell coverage where thetransmission/reception points created by the RRHs have different cellidentifiers (IDs) from the macro cell, and 4) a heterogeneous networkwith low power RRHs within the macro cell coverage where thetransmission/reception points created by the RRHs have the same cell IDsas the macro cell. The CoMP communication schemes that have beenidentified as the focus for standardization are joint transmission (JT);dynamic point selection (DPS), including dynamic point blanking; andcoordinated scheduling/beamforming, including dynamic point blanking.Further description of the CoMP usage scenarios is included in 3GPP TS36.819, which is expressly incorporated by reference herein.

Accordingly, there is a need for improved techniques in the CoMPcommunication schemes.

SUMMARY

Embodiments of the present disclosure provide CSI definitions andfeedback modes for CoMP.

In one embodiment, a method for CSI feedback reporting by a UE in a CoMPcommunication system is provided. The method includes identifying, whendownlink transmissions to the UE are configured with at least two CSIsubframe subsets, an interference measurement resource within one of theCSI subframe subsets belonging to a CSI reference resource. The methodalso includes using the identified interference measurement resource toderive an interference measurement.

In another embodiment, a method for receiving CSI feedback reporting bybase station in a CoMP communication system is provided. The methodincludes receiving, in an uplink control information transmissions froma UE, CSI feedback based on an interference measurement. Downlinktransmissions to the UE are configured with at least two CSI subframesubsets. The interference measurement is derived using an interferencemeasurement resource identified within one of the CSI subframe subsetsbelonging to a CSI reference resource.

In yet another embodiment, an apparatus in a UE capable of CSI feedbackreporting in a CoMP communication system is provided. The apparatusincludes a controller configured to, when downlink transmissions to theUE are configured with at least two CSI subframe subsets, identify aninterference measurement resource within one of the CSI subframe subsetsbelonging to a CSI reference resource; and to use the identifiedinterference measurement resource to derive an interference measurement.

In another embodiment, an apparatus for receiving channel stateinformation (CSI) feedback reporting by base station in a CoMPcommunication system is provided. The apparatus includes a receiverconfigured to receive, in an uplink control information transmissionfrom a UE, CSI feedback information based on an interferencemeasurement. Downlink transmissions to the UE are configured with atleast two CSI subframe subsets. The interference measurement is derivedusing an interference measurement resource identified within one of theCSI subframe subsets belonging to a CSI reference resource.

In one or more of the embodiment, if the UE is configured with multipleinterference measurement resources, the CSI configurations may eachinclude an associated CSI reference signal resource index andinterference measurement resource index pair. Each CSI configuration maybe for a particular TP or CSI process.

In one or more of the embodiment, independent periodic physical unlinkcontrol channel (PUCCH) for multiple CSI configurations is provided. Inthis embodiment, the periodic feedback mode parameters are set upindependently for two or more CSI configurations

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 illustrates an exemplary wireless system which transmits messagesin accordance with an illustrative embodiment of the present disclosure;

FIG. 2 illustrates a high-level diagram of an orthogonal frequencydivision multiple access transmit path in accordance with anillustrative embodiment of the present disclosure;

FIG. 3 illustrates a high-level diagram of an orthogonal frequencydivision multiple access receive path in accordance with an illustrativeembodiment of the present disclosure;

FIG. 4 illustrates a block diagram of a transmitter and a receiver in awireless communication system that may be used to implement variousembodiments of the present disclosure;

FIG. 5 illustrates a block diagram of a CoMP communication system inaccordance with various embodiments of the present disclosure;

FIG. 6 illustrates feedback reporting corresponding to multiple CSI-RSresources which may be multiplexed in time in accordance with anexemplary embodiment;

FIG. 7 illustrates feedback reporting for multiple CSI-RS resourceswhich may be configured together for certain report types in accordancewith an exemplary embodiment;

FIGS. 8A and 8B illustrate examples of a single periodic PUCCHconfigured with UE autonomous TP switching in accordance withillustrative embodiments of the present disclosure;

FIGS. 9A and 9B illustrate examples of a reference subframe with aconfiguration of IM resource and CSI subframe subsets in accordance withvarious embodiments of the present disclosure; and

FIG. 10 illustrates a process for CSI feedback reporting by a UE in acoordinated multipoint communication system in accordance with variousembodiments of the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 10, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

The following standards documents are incorporated by referenceherein: 1) 3GPP TS 36.211 v10.1.0, “E-UTRA, Physical channels andmodulation;” 2) 3GPP TS 36.212 v10.1.0, “E-UTRA, Multiplexing andChannel coding;” 3) 3GPP TS 36.213 v10.1.0, “E-UTRA, Physical LayerProcedures;” 4) RP-111365 Coordinated Multi-Point Operation for LTE WID;and 5) 3GPP TR 36.819 V11.0.0 (2011-09).

FIGS. 1-3 below describe various embodiments implemented in wirelesscommunication systems and with the use of OFDM or OFDMA communicationtechniques. The description of FIGS. 1-3 is not meant to imply physicalor architectural limitations to the manner in which differentembodiments may be implemented. Different embodiments of the presentdisclosure may be implemented in any suitably arranged communicationssystem.

FIG. 1 illustrates exemplary wireless system 100, which transmitsmessages according to the principles of the present disclosure. In theillustrated embodiment, wireless system 100 includes transmission points(e.g., an Evolved Node B (eNB), Node B), such as base station (BS) 101,base station (BS) 102, base station (BS) 103, and other similar basestations or relay stations (not shown). Base station 101 is incommunication with base station 102 and base station 103. Base station101 is also in communication with network 130 or a similar IP-basedsystem (not shown).

Base station 102 provides wireless broadband access (via base station101) to network 130 to a first plurality of UEs (e.g., mobile phone,mobile station, subscriber station) within coverage area 120 of basestation 102. The first plurality of UEs includes UE 111, which may belocated in a small business (SB); UE 112, which may be located in anenterprise (E); UE 113, which may be located in a WiFi hotspot (HS); UE114, which may be located in a first residence (R); UE 115, which may belocated in a second residence (R); and UE 116, which may be a mobiledevice (M), such as a cell phone, a wireless laptop, a wireless PDA, orthe like.

Base station 103 provides wireless broadband access (via base station101) to network 130 to a second plurality of UEs within coverage area125 of base station 103. The second plurality of UEs includes UE 115 andUE 116. In an exemplary embodiment, base stations 101-103 maycommunicate with each other and with UEs 111-116 using OFDM or OFDMAtechniques.

While only six UEs are depicted in FIG. 1, it is understood thatwireless system 100 may provide wireless broadband access to additionalUEs. It is noted that UE 115 and UE 116 are located on the edges of bothcoverage area 120 and coverage area 125. UE 115 and UE 116 eachcommunicate with both base station 102 and base station 103 and may besaid to be operating in handoff mode, as known to those of skill in theart.

UEs 111-116 may access voice, data, video, video conferencing, and/orother broadband services via network 130. In an exemplary embodiment,one or more of UEs 111-116 may be associated with an access point (AP)of a WiFi WLAN. UE 116 may be any of a number of mobile devices,including a wireless-enabled laptop computer, personal data assistant,notebook, handheld device, or other wireless-enabled device. UEs 114 and115 may be, for example, a wireless-enabled personal computer (PC), alaptop computer, a gateway, or another device.

FIG. 2 is a high-level diagram of transmit path circuitry 200. Forexample, the transmit path circuitry 200 may be used for an orthogonalfrequency division multiple access (OFDMA) communication. FIG. 3 is ahigh-level diagram of receive path circuitry 300. For example, thereceive path circuitry 300 may be used for an orthogonal frequencydivision multiple access (OFDMA) communication. In FIGS. 2 and 3, fordownlink communication, the transmit path circuitry 200 may beimplemented in base station (BS) 102 or a relay station, and the receivepath circuitry 300 may be implemented in a UE (e.g., UE 116 of FIG. 1).In other examples, for uplink communication, the receive path circuitry300 may be implemented in a base station (e.g., base station 102 ofFIG. 1) or a relay station, and the transmit path circuitry 200 may beimplemented in a UE (e.g., UE 116 of FIG. 1).

Transmit path circuitry 200 comprises channel coding and modulationblock 205, serial-to-parallel (S-to-P) block 210, Size N Inverse FastFourier Transform (IFFT) block 215, parallel-to-serial (P-to-S) block220, add cyclic prefix block 225, and up-converter (UC) 230. Receivepath circuitry 300 comprises down-converter (DC) 255, remove cyclicprefix block 260, serial-to-parallel (S-to-P) block 265, Size N FastFourier Transform (FFT) block 270, parallel-to-serial (P-to-S) block275, and channel decoding and demodulation block 280.

At least some of the components in FIGS. 2 and 3 may be implemented insoftware, while other components may be implemented by configurablehardware or a mixture of software and configurable hardware. Inparticular, it is noted that the FFT blocks and the IFFT blocksdescribed in this disclosure document may be implemented as configurablesoftware algorithms, where the value of Size N may be modified accordingto the implementation.

Furthermore, although this disclosure is directed to an embodiment thatimplements the Fast Fourier Transform and the Inverse Fast FourierTransform, this is by way of illustration only and should not beconstrued to limit the scope of the disclosure. It will be appreciatedthat in an alternate embodiment of the disclosure, the Fast FourierTransform functions and the Inverse Fast Fourier Transform functions mayeasily be replaced by Discrete Fourier Transform (DFT) functions andInverse Discrete Fourier Transform (IDFT) functions, respectively. Itwill be appreciated that for DFT and IDFT functions, the value of the Nvariable may be any integer number (i.e., 1, 2, 3, 4, etc.), while forFFT and IFFT functions, the value of the N variable may be any integernumber that is a power of two (i.e., 1, 2, 4, 8, 16, etc.).

In transmit path circuitry 200, channel coding and modulation block 205receives a set of information bits, applies coding (e.g., LDPC coding)and modulates (e.g., Quadrature Phase Shift Keying (QPSK) or QuadratureAmplitude Modulation (QAM)) the input bits to produce a sequence offrequency-domain modulation symbols. Serial-to-parallel block 210converts (i.e., de-multiplexes) the serial modulated symbols to paralleldata to produce N parallel symbol streams where N is the IFFT/FFT sizeused in BS 102 and UE 116. Size N IFFT block 215 then performs an IFFToperation on the N parallel symbol streams to produce time-domain outputsignals. Parallel-to-serial block 220 converts (i.e., multiplexes) theparallel time-domain output symbols from Size N IFFT block 215 toproduce a serial time-domain signal. Add cyclic prefix block 225 theninserts a cyclic prefix to the time-domain signal. Finally, up-converter230 modulates (i.e., up-converts) the output of add cyclic prefix block225 to RF frequency for transmission via a wireless channel. The signalmay also be filtered at baseband before conversion to RF frequency.

The transmitted RF signal arrives at UE 116 after passing through thewireless channel, and reverse operations to those at BS 102 areperformed. Down-converter 255 down-converts the received signal tobaseband frequency, and remove cyclic prefix block 260 removes thecyclic prefix to produce the serial time-domain baseband signal.Serial-to-parallel block 265 converts the time-domain baseband signal toparallel time-domain signals. Size N FFT block 270 then performs an FFTalgorithm to produce N parallel frequency-domain signals.Parallel-to-serial block 275 converts the parallel frequency-domainsignals to a sequence of modulated data symbols. Channel decoding anddemodulation block 280 demodulates and then decodes the modulatedsymbols to recover the original input data stream.

Each of base stations 101-103 may implement a transmit path that isanalogous to transmitting in the downlink to UEs 111-116 and mayimplement a receive path that is analogous to receiving in the uplinkfrom UEs 111-116. Similarly, each one of UEs 111-116 may implement atransmit path corresponding to the architecture for transmitting in theuplink to base stations 101-103 and may implement a receive pathcorresponding to the architecture for receiving in the downlink frombase stations 101-103.

FIG. 4 illustrates a block diagram of a transmitter 405 and a receiver410 in a wireless communication system that may be used to implementvarious embodiments of the present disclosure. In this illustrativeexample, the transmitter 405 and the receiver 410 are devices at acommunication point in a wireless communication system, such as, forexample, wireless system 100 in FIG. 1. In some embodiments, thetransmitter 405 or the receiver 410 may be a network entity, such as abase station, e.g., an evolved node B (eNB), a remote-radio head, arelay station, an underlay base station; a gateway (GW); or a basestation controller (BSC). In other embodiments, the transmitter 405 orthe receiver 410 may be a UE (e.g., mobile station, subscriber station,etc.). In one example, the transmitter 405 or the receiver 410 is anexample of one embodiment of the UE 116 in FIG. 1. In another example,the transmitter 405 or the receiver 410 is an example of one embodimentof the base station 102 in FIG. 1.

The transmitter 405 comprises antenna(s) 415, phase shifters 420, Txprocessing circuitry 425, and controller 430. The transmitter 405receives analog or digital signals from outgoing baseband data.Transmitter 405 encodes, multiplexes, and/or digitizes the outgoingbaseband data to produce a processed RF signal that is sent and/ortransmitted via transmitter 405. For example, the Tx processingcircuitry 425 may implement a transmit path that is analogous to thetransmit processing circuitry 200 in FIG. 2. Transmitter 405 may alsoperform spatial multiplexing via layer mapping to different antennas inantenna(s) 415 to transmit signals in multiple different beams. Thecontroller 430 controls the overall operation of transmitter 405. In onesuch operation, controller 430 controls the transmission of signals bythe transmitter 405 in accordance with well-known principles.

Receiver 410 receives from antenna(s) 435 an incoming RF signal orsignals transmitted by one or more transmission points, such as basestations, relay stations, remote radio heads, UEs, etc. Receiver 410includes Rx processing circuitry 445 that processes the receivedsignal(s) to identify the information transmitted by the transmissionpoint(s). For example, the Rx processing circuitry 445 may down-convertthe incoming RF signal(s) to produce an intermediate frequency (IF) or abaseband signal by channel estimating, demodulating, stream separating,filtering, decoding, and/or digitizing the received signal(s). Forexample, the Rx processing circuitry 445 may implement a receive paththat is analogous to the receive processing circuitry 300 in FIG. 3. Thecontroller 450 controls the overall operation of the receiver 410. Inone such operation, the controller 450 controls the reception of signalsby the receiver 410 in accordance with well-known principles.

In various embodiments, the transmitter 405 is located within a TP, andthe receiver is located within a UE in a CoMP communication system. Forexample, in the CoMP communication, multiple TPs may includetransmitters similar to the transmitter 405 that transmits to the UE.The multiple TPs may be any combination of base stations (e.g., eNB,macro base stations, etc.), RRHs, and/or underlay base stations (e.g.,micro base stations, relay stations, etc.).

The illustration of transmitter 405 and receiver 410 illustrated in FIG.4 is for the purposes of illustrating one embodiment in whichembodiments of the present disclosure may be implemented. Otherembodiments of the transmitter 405 and the receiver 410 may be usedwithout departing from the scope of this disclosure. For example, thetransmitter 405 may be located in a communication node (e.g., BS, UE,RS, and RRH) that also includes a receiver, such as receiver 410.Similarly, the receiver 410 may be located in a communication node(e.g., BS, UE, RS, and RRH) that also includes a transmitter, such astransmitter 405. Antennas in the Tx and Rx antenna arrays in thiscommunication node may overlap or be the same antenna arrays used fortransmission and reception via one or more antenna switching mechanisms.

FIG. 5 illustrates a block diagram of a CoMP communication system 500 inaccordance with various embodiments of the present disclosure. In thisillustrative example, the CoMP communication system 500 includes a UE505 and two TPs 510 and 515. For example, the UE 505 may include areceiver and transmitter as illustrated in FIG. 4. The TPs 510 and 515may also include a receiver and transmitter as illustrated in FIG. 4.The TPs 510 and 515 may be any combination of base stations (e.g., eNB,macro base stations, etc.), RRHs, and/or underlay base stations (e.g.,micro base stations, relay stations, etc.). Additionally, other TPs andUEs may be present in the CoMP communication system 500. For example,more than two TPs may communicate with the same UE 505.

The TPs 510 and 515 are connected to a network 520. For example, the TPs510 and 515 may be connected by a wire line and/or fiber opticalnetwork. The network 520 provides connections between the TPs 510 and515 to provide data and control information for wireless communicationbetween the TPs 510 and 515 and the UE 505. The network 520 performsscheduling for wireless communications in the CoMP communication system500. For example, the network 520 may include one or more gateways; orbase station controllers. In one example, the network 520 may be oneembodiment of the network 130 in FIG. 1.

With the different CoMP transmission schemes described in the backgroundabove, the network 520 needs to know the channel quality indicator(CQI), precoding matrix indicator (PMI), and rank indicator (RI)supported by the UE to optimize scheduling. The feedback definitions andmeasurements are defined for a single-cell transmission for LIE Release8 to Release 10. The individual CoMP scheme performance may also becharacterized by other parameters, such as the TPs used in the CoMPscheme; precoding applied at each of the one or more transmitting TPs;the TPs that are blanked or not transmitting; and the interferencemeasurement resource that may be configured for measurement ofindividual CQIs.

A CSI reference signal (RS) enables channel measurements by a UE. A UEspecific CSI-RS configuration includes: 1) a non-zero power CSI-RSresource; and 2) one or more zero-power CSI-RS resources. Typically, thenon-zero power CSI-RS resource corresponds to the antenna elements/portsof the serving cell. Zero-power CSI-RS, also commonly referred to asmuted CSI-RS, are used to protect the CSI-RS resources of another cell,and a UE is expected to rate match (skip for decoding/demodulation)around these resources. Additional configuration details of the CSI-RSare specified in 3GPP TS 36.211, particularly in sections 6.10.5 and7.2.5.

To support CoMP transmission, a network needs feedback corresponding tomultiple transmission points or cells. As a result, a network can set upmultiple CSI-RS resources, each typically corresponding to a TP or CSIprocess. Unless otherwise stated, the terms “CSI-RS resource,” “TP,” and“CSI process” may be used interchangeably. Further details of CSI-RSresource configurations and the configurable parameters for each CSI-RSresource may include that configuration of multiple non-zero-powerCSI-RS resources include at least: AntennaPortsCount, ResourceConfig,SubframeConfig, P_(c), and a Parameter X to derive scramblinginitialization c_(init)=2¹⁰·(7·(n_(s)+1)+l+1)·(2·X+1)+2·X+N_(CP). Xranges from 0 to 503 and can be interpreted as virtual cell id. InRelease 10, X is the PCI of the serving cell. These parameters areconfigured per CSI-RS resource. Some parameters may be configured perCSI-RS port considering the decision of supporting coherent jointtransmission by the aggregate CSI feedback corresponding to multiple TPsin one CSI-RS resource. While the CSI-RS resources capture channels ofindividual TPs, the interference measurement also depends on the CoMPscheme. In Releases 8-10, a single interference measurement resource isused, which is the cell-specific reference signal (CRS) itself.Interference measurement on CRS captures all the interference outsidethe cell.

For CoMP, one or more interference measurement resources can be definedto capture the interference for a hypothetical CoMP scheme. At least oneInterference Measurement Resource (IMR) (also referred to as aCSI-interference measurement (IM) resource or CSI-IM resource) can beconfigured for a Release-11 UE. A maximum of only one or multiple IMRsmay be configured for a Release-11 UE. Each IMR may consist of only REs,which can be configured as Release 10 CSI-RS resources.

For support of CoMP, new CSI-RS configurations are defined and signaledby higher layers as described herein in accordance with the variousembodiments of the present disclosure. In Release-10 and, morespecifically, 3GPP TS 36.331, CSI-RS configuration is signaled asfollows, where a single non-zero power CSI-RS and its parameters areindicated, while multiple zero-power CSI-RS configurations are indicatedusing a bitmap.

With one or more interference measurement resources supported for CoMP,CSI measurement is based on both a CSI-RS resource and an IMR or CSI-IMresource. As a result, embodiments of the present disclosure define CSIconfigurations for feedback.

In various embodiments, if the UE is configured with multiple IMRresources, the CSI configurations can be defined as illustrated in Table1 below, each with an associated (CSI-RS resource index, IMR resourceindex) pair. Each CSI configuration may be for a particular TP or CSIprocess.

TABLE 1 CSI Configuration CSI-RS Resource Index IMR Resource IndexConfiguration 1 X1 Y1 Configuration 2 X2 Y2

In various embodiments, the IMR resource index may be based on one ofthe currently defined 16 CSI-RS resource configurations that are usedfor zero-power CSI-RS in Release-10 based on a 4Tx CSI-RS pattern (e.g.,such as the four CSI reference signal column in Table 6.10.5.2-1. of36.211).

In other embodiments, an antenna port count can be additionallyindicated to allow configuration of any of the 1 or 2, 4, 8 Tx patterns.In other embodiments, instead of indicating antenna port count, theconfiguration of any of the 1 or 2, 4, 8 Tx patterns can be allowed byusing an aggregate bit field, i.e., a single bit field to indicate atotal of 32 (1 or 2 Tx)+16 (4Tx)+8 (8 Tx)=56 patterns. Multiple such CSIconfigurations can be defined for a UE for CSI feedback purposes.

In other embodiments, a single IMR resource can be configured, while themultiple CSI-RS resources are configured separately. In this case, eachCSI-RS configuration is defined by the associated CSI-RS resource and atleast the common IMR resource. The whole set of configurations (1, 2, 4,8 Tx) patterns may be using either an antennaportscount parameter or anaggregate IMRresourceconfig parameter.

In some embodiments, one or more IMR resources may be configured usingthe definitions above. In some embodiments, a list of IMR resources canbe set up using a single field. In other embodiments, an interferencemeasurement hypothesis may be based on at least one IMR resource and atleast one non-zero power CSI-RS resource. In this case, the UE isexpected to measure interference on an IMR resource by just summing oraveraging received signal power contribution of corresponding REs. Forderiving the interference measurement component from non-zero powerCSI-RS resources, the UE performs channel estimation and derives theinterference power based on the sum or average power of the CSI-RS portscorresponding to the non-zero-power CSI-RS resource.

Table 2 below illustrates an example with an IMR resource Y asconfigured in the examples above. Such CSI configuration may be set updifferently for periodic and aperiodic feedback modes.

TABLE 2 CSI-RS IMR Resource configuration (IMR Resource Resource Index,Non Zero Power CSI- CSI Configuration Index RS Resource ConfigurationIndex) Configuration 1 X1 (Y, Z1) Configuration 2 X2 (Y, Z2)

The non-zero power CSI-RS (Z1, Z2) resources used may be implicitlyknown by the UE based on the feedback mode or explicitly configured asin Table 2 above. In one example for implicit configuration, thenon-zero power CSI-RS resources (Z1 for configuration 1) used forinterference measurement may include some or all of the non-zero powerCSI-RS configured for that UE. In another example, the non-zero powerCSI-RS resources used for interference measurement for a CSIconfiguration may be implicitly based on the corresponding CSI-RSresource index (X1 for configuration 1). An example of such a method isthat the non-zero power CSI-RS resources (Z1) used for interferencemeasurement are all the configured CSI-RS resources for that UE exceptX1. In another example, the non-zero power CSI-RS resources (Z1) usedfor interference measurement may be all the CSI-RS resources configuredfor that UE except those corresponding to the CSI configurations forthat UE (i.e., X1, X2). For example, (X1, X2) may be considered areporting set, while X1 may be considered a transmission set for CSIpurposes.

In various embodiments, the PDSCH is not mapped to the REs correspondingto the configured IMR resource(s). The rules for PDSCH mapping toresource elements are outlined in section 6.3.5 of 36.211. Embodimentsof the present disclosure include that for each of the antenna portsused for transmission of the physical channel, the block ofcomplex-valued symbols y^((p))(0), . . . , y^((p))(M_(symb) ^(ap)−1)shall conform to the downlink power allocation specified in section 5.2and be mapped in sequence starting with y^((p))(0) to resource elements(k, l) which, among other criteria, are not used for transmission of IMRreference signals and the DCI associated with the downlink transmissionuses the C-RNTI or semi-persistent C-RNTI.

In addition to the CSI and IMR (or CSI-IM resource) configurations,embodiments of the present disclosure also provide CQI definitions. Inone example, the CQI definition is modified as follows. In the CSIreference resource, the UE shall assume the following for the purpose ofderiving the CQI index, and if also configured, PMI and RI: the first 3OFDM symbols are occupied by control signaling; no resource elementsused by primary or secondary synchronization signals or PBCH; CP lengthof the non-MBSFN subframes; Redundancy Version 0; if CSI-RS is used forchannel measurements, the ratio of PDSCH EPRE to CSI-RS EPRE is as givenin Section 7.2.5 of 3GPP TS 36.213. Additionally, for transmission modex, which is a new transmission mode defined to enable CoMP support forLTE, CSI reporting: CRS REs are as in non-MBSFN subframes; if the UE isconfigured for PMI/RI reporting, the UE-specific reference signaloverhead is consistent with the most recent reported rank; and PDSCHsignals on antenna ports {7 . . . 6+v} for vlayers results in signalsequivalent to corresponding symbols transmitted on antenna ports {a₁ . .. a_(P)} of the CSI-RS resource, as given by

${\begin{bmatrix}y^{a_{1}} \\\vdots \\\vdots \\y^{a_{P}}\end{bmatrix} = {{W(i)}\begin{bmatrix}{x^{(0)}(i)} \\\vdots \\\vdots \\{x^{({v - 1})}(i)}\end{bmatrix}}},$

where x(i)=[x⁰(i) . . . x^((v-1)(i)]) ^(T) is a vector of symbols fromthe layer mapping in section 6.3.3.2 of 3GPP TS 36.211, Pε{1, 2, 4, 8}is the number of CSI-RS ports configured for the CSI-RS resource, and ifonly one CSI-RS port is configured, W(i) is 1, otherwise W(i) is theprecoding matrix corresponding to the reported PMI applicable to x(i).The corresponding PDSCH signals transmitted on antenna ports {a₁ . . .a_(P)} has a ratio of EPRE to CSI-RS EPRE equal to the ratio given insection 7.2.5 of 3GPP TS 36.213. If IMR based interference measurementis configured for the UE, assume the interference is the sum ofinterference observed on the IMR resource and one or more non-zero powerCSI-RS resources configured for the CQI measurement (i.e., associatedwith the CSI request or higher layer configuration), where theindividual contributions are obtained as: for interference measurementbased on a non-zero power CSI-RS resource, the interference is based onthe [average] received power on the reference signals corresponding tothe CSI-RS antenna ports of the CSI-RS resource; and for interferencemeasurement based on an IMR resource, the interference measurement isthe total power (or average power) observed on the REs corresponding tothe IMR resource. Further, in the CSI reference resource, the UE shallassume the following for the purpose of deriving the CQI index, and ifalso configured, PMI and RI: no REs allocated for CSI-RS and zero-powerCSI-RS and IMR resources; no REs allocated for PRS; and the PDSCHtransmission scheme given by Table 7.2.3-0 of 3GPP TS 36.213, dependingon the transmission mode currently configured for the UE (which may bethe default mode).

In various embodiments, the interference measurement may only beperformed if an IMR resource is configured by higher layers. In thiscase, the condition for interference measurement in the CQI definitioncan be modified as if at least one IMR resource is configured by higherlayers for the UE. In other embodiments, if the CSI configurationcorresponding to the CQI requested as part of a periodic feedback modeor an aperiodic CSI request has a configured IMR resource, theninterference measurement may be defined with the condition if at leastone IMR resource is configured as part of the periodic CSI configurationor aperiodic CSI request. If interference measurement based on anon-zero power CSI-RS resource is not supported, then the text in theCQI definition can be modified as if IMR based interference measurementis configured for the UE, assume the interference is based on an IMRresource, where the interference is the total power (or average power)observed on the REs corresponding to the IMR resource. The same orsimilar modifications outlined above may be applied to this case as wellfor the condition to trigger IMR based interference assumption.

In accordance with the above definitions for multiple CSI and/or IMRconfigurations, embodiments of the present disclosure provide forperiodic feedback modes based on the PUCCH. Periodic feedback modes arebased on semi-persistent configuration of uplink control information onthe PUCCH channel. These feedback modes are configured with a certainperiodicity and offset. The supported feedback modes, individual reporttypes, and timing configuration (periodicity, offset) are summarized in3GPP TS 36.213 Table 7.2.2-1. Additionally, various CQI/PMI and RIreporting types with distinct periods and offsets are supported for thePUCCH CSI reporting modes as given in 3GPP TS 36.213 Table 7.2.2-3.

For each serving cell, the periodicity N_(pd) (in subframes) and offsetN_(OFFSET,CQI) (in subframes) for CQI/PMI reporting are determined basedon the parameter cqi-pmi-ConfigIndex (I_(CQI/PMI)) given in 3GPP TS36.213 Table 7.2.2-1A for frequency division duplex (FDD) and 3GPP TS36.213 Table 7.2.2-1C for time division duplex (TDD). The periodicityM_(RI) and relative offset N_(OFFSET,RI) for RI reporting are determinedbased on the parameter ri-ConfigIndex (I_(RI)) given in 3GPP TS 36.213Table 7.2.2-1B. Both cqi-pmi-ConfigIndex and ri-ConfigIndex areconfigured by higher layer signaling. The relative reporting offset forRI N_(OFFSET,RI) takes values from the set {0, −1, . . . , −(N_(pd)−1)}.If a UE is configured to report for more than one CSI subframe set, thenparameter cqi-pmi-ConfigIndex and ri-ConfigIndex respectively correspondto the CQI/PMI and RI periodicity and relative reporting offset forsubframe set 1 and cqi-pmi-ConfigIndex2 and ri-ConfigIndex2 respectivelycorrespond to the CQI/PMI and RI periodicity and relative reportingoffset for subframe set 2.

As an example, the wideband CQI/PMI reporting timing is defined asfollows based on configured timing parameters. Similar definitions aredefined in 36.213 for other report types. In the case where widebandCQI/PMI reporting is configured: the reporting instances for widebandCQI/PMI are subframes satisfying(10×n_(f)+└n_(s)/2┘−N_(OFFSET,CQI))mod(N_(pd))=0. In case RI reportingis configured, the reporting interval of the RI reporting is an integermultiple M_(RI) of period N_(pd) (in subframes). The reporting instancesfor RI are subframes satisfying(10×n_(f)+└n_(s)/2┘−N_(OFFSET,CQI)−N_(OFFSET,RI))mod(N_(pd)·M_(RI))=0.

To support CoMP transmissions, embodiments of the present disclosure setup feedback corresponding to more than one CSI-RS configurations(resources, CSI processes, or TPs) and define new feedback modes forthis purpose. As used herein, a CSI configuration means a (CSI-RSresource, IMR resource) pair. However, with a single IMR resource, a CSIconfiguration may be simply replaced by the CSI-RS resource.

In one embodiment, independent periodic PUCCH for multiple CSIconfigurations is provided. In this embodiment, the periodic feedbackmode parameters are set up independently for two or more CSIconfigurations. This embodiment is suitable, for example, when nointer-CSI-RS feedback is needed. Inter-CSI-RS resource feedback refersto feedback which relies on measurement of more than one CSI-RSresource. Additional examples of inter-CSI-RS resource feedback aredescribed below.

When two or more periodic reports are configured, the timing parameterschosen may result in a collision of certain reports. Such a collisionmay be avoidable sometimes by the appropriate choice of parameters bythe scheduler, but may not always be avoidable due to schedulingflexibility issues. Embodiments of the present disclosure providedifferent ways to handle such a collision. The methods and embodimentsdescribed below can also apply to UEs configured with multiple componentcarriers when two or more periodic CSIs reporting for the multiplecomponent carriers are scheduled in a same subframe.

In various embodiments, only one of the reports may be sent andremaining reports may be dropped (i.e., not transmitted). In thissituation, dropping rules are defined, which are clear to both the UEand the eNB. In one embodiment, in case of collision between two PUCCHreports for different CSI-RS resources, the UE may drop the feedbackbased on report type. In one embodiment, the report to be transmitted isselected based on the report type. For example, an RI report may beconsidered more useful than other CQI/PMI reports, and a widebandCQI/PMI report may be prioritized over a subband CQI/PMI report. In sucha case, a priority order is defined for each report. As an example,reporting types 3, 5, or 6 may have higher priority over reporting types1, 1a, 2, 2a, 2b, 2c, or 4. So, if a report type for a first CSI-RSresource is type 3 and report type for a second CSI-RS resource is type1, then the report corresponding to the first CSI-RS resource isprioritized to be sent.

In another embodiment, in case of collision between two PUCCH reportsfor different CSI-RS resources, the UE may drop the feedback based onCSI-RS transmission. As discussed above, each CSI-RS resource has aunique subframe configuration parameterized by a periodicity and timingoffset when the corresponding CSI-RS are sent. In one method, thereports corresponding to different CSI-RS resources are prioritizedbased on the timing relationship with past CSI-RS transmissions of thecorresponding resources. In another method, the report corresponding tothe CSI-RS resource with the most recent CSI-RS transmission isprioritized, since the corresponding CSI is more useful (consideringtime variation of CSI).

In another embodiment, in case of collision between two PUCCH reportsfor different CSI-RS resources, the UE may drop the feedback based onthe CSI-RS resource with best performance. In one method, the reportcorresponding to the CSI-RS resource is prioritized based on theperformance attributed to the CSI-RS resource. In one method, theprioritization may be based on CQI (wideband or subband). Since thenetwork may not be aware of the current CQI, in one method, an index ofthe chosen CSI-RS resource is reported. In another method, to avoidadditional reporting, the prioritization may be based on the mostrecently reported wideband CQI of each report. In another method, otherfeedback parameters may also be used like RI as a performance metric. Inanother method, the choice of the CSI-RS for reporting may be based onthe corresponding RSRP or RSRQ if an RSRP type metric can be associatedwith a CSI-RS configuration. Such RSRP may be separately reported by theUE and known to eNB.

In another embodiment, in case of collision between two PUCCH reportsfor different CSI-RS resources, the UE may drop the feedback based onthe CSI-RS resource index. In one method, the prioritization of a reportcorresponding to a CSI-RS resource may be simply based on the CSI-RSresource index. Multiple CSI-RS resources are configured by RRC (higherlayer) signaling, thereby implicitly associating an index (from thesignaled order) to each of the CSI-RS resources. This allows the networkto prioritize a CSI-RS resource by network configuration. Suchprioritization/indexing may be affected by the scheduling aspects and/orsignal strength measured by the network for the corresponding CSI-RSresource.

In another embodiment, in case of collision between two PUCCH reportsfor different CSI-RS resources, the UE may drop the feedback based onreporting mode parameters. In one method, the prioritization of thereports is based on the feedback mode setup parameters like periodicityand offset (Npd, Noffset).

In other embodiments, when the multiple CSI reports corresponding to twoor more CSI-RSs collide, all the CSI reports are multiplexed and senttogether. Different approaches can be used for multiplexing. Forexample, the reports may be multiplexed based on PUCCH Format 3. Thoughthe individual reports are transmitted based on different PUCCH formats,in the event of collision, multiple reports are multiplexed into asingle report using the higher capacity PUCCH channel format 3, whichcan support <=22 bits. In one method, when more than three reportscollide, two of the reports are multiplexed and the rest of the reportsare dropped. The prioritization for selecting the multiplexed reportsand the dropped reports may follow one or more dropping rules discussedpreviously. In another method, the number of reports multiplexed is suchthat they can be supported by the format size of the PUCCH format 3. Forexample, three RI reports (<=3 bits each) can be accommodated in asingle PUCCH Format 3 report. In one method, whether to multiplex usingPUCCH Format 3 or drop the reports (except one) may be based on the linkquality of the UE. In one method, whether to multiplex using PUCCHFormat 3 or drop the reports (except one) may be configured by higherlayers.

In other examples, whether the reports are to be multiplexed may beconditioned on the physical uplink shared channel (PUSCH). The networkmay control the behavior in the event of collision. In one method, aPUSCH resource may be scheduled for the UE for transmission on uplinkcontrol information (UCI) (or CSI) in that sub-frame. If a UL grant forsuch a PUSCH resource is detected, the UE transmits the multiplexedreport on the PUSCH (which has a larger capacity than PUCCH). If nogrant for PUSCH resource is detected, the UE simply drops one or morereports, for example, according to the dropping rules described above.More generally, the multiplexing/dropping behavior may be based on theconfiguration and the size of the PUSCH resource (e.g., two or threereports may be multiplexed based on the PUSCH resource size and/orconfiguration).

The network may also semi-statically configure PUSCH resources, sincethe network is aware of the collision instances. In such examples, if aPUSCH resource is configured in a sub-frame with collision event,multiplexing of reports may be used. Otherwise, CSI dropping may beused, for example, according to the dropping rules described above. Ifthe UL grant for such a configured PUSCH resource has non-zero value fora CSI request field, then a periodic CSI report as configured by CSIrequest is transmitted and periodic CSI is dropped. If the UL grant forsuch a configured PUSCH resource has zero value for CSI request field,and in the event of collision of two or more CSI reports, then theperiodic CSI report is sent by multiplexing the CSI reports as describedabove. In one method, even if simultaneous transmission of PUCCH andPUSCH is configured, in case of collision of periodic CSI reports, boththe CSI and data are multiplexed on PUSCH.

In some cases, other control information on the uplink, such as ACK/NACKfeedback, may collide with CSI. In this case, the dropping andmultiplexing rules may be further modified by such an event. In onemethod, if the UE is configured with simultaneous PUCCH/PUSCHtransmission, in the event of collision of periodic PUCCH CSI reports,the CSI is transmitted on a scheduled PUSCH resource and ACK/NACK istransmitted on the PUCCH resource configured for ACK/NACK (e.g., PUCCHformat 1a/1b/3). If the UE is not configured for simultaneousPUCCH/PUSCH transmission and in the event of collision of periodic PUCCHCSI reports, the CSI and ACK/NACK are transmitted on a scheduled PUSCH.

In other examples, whether the reports are to be multiplexed may bebased on semi-statically configured PUCCH Format 3. In one method, anetwork may semi-statically configure a PUCCH Format 3 resource, sincethe network is aware of the collision instances. If such a configuredPUCCH Format 3 resource is available, a UE may multiplex the CSI in theconfigured PUCCH Format 3 or drop CSIs according to the dropping rulesdescribed above.

In some cases, other control information on the uplink like ACK/NACKfeedback may collide with CSI. In this case, the dropping andmultiplexing rules may be further modified by such an event. In onemethod, if an ACK/NACK (or SR) collides with CSI, one or more of the CSImay be multiplexed with the ACK/NACK using PUCCH Format 3 configured forACK/NACK. In another method, if an ACK/NACK (or SR) collides with CSI,one or more of the CSI may be multiplexed with the ACK/NACK using PUCCHFormat 3 configured for CSI. This behavior may be dependent upon thehigher-layer configured value of simultaneousAckNackAndCQI. For example,ACK/NACK and CSI may be multiplexed if simultaneousAckNackAndCQI==TRUE,while only ACK/NACK is transmitted on the PUCCH Format 3 configured forACK/NACK with dropping CQI if simultaneousAckNackAndCQI=FALSE. Inanother method, if the UE is configured with simultaneous PUCCH/PUSCHtransmission, in the event of collision of periodic PUCCH CSI reports ina subframe in which a PUSCH is scheduled, the CSI is transmitted on ascheduled PUSCH resource and ACK/NACK is transmitted on the PUCCHresource configured for ACK/NACK. If the UE is not configured withsimultaneous PUCCH/PUSCH transmission, in the event of collision ofperiodic PUCCH CSI reports in a subframe in which a PUSCH is scheduled,the CSI and ACK/NACK are transmitted on a scheduled PUSCH resource.

Embodiments of the present disclosure provide joint configuration ofmultiple periodic reports. In various embodiments, in the presence ofsome reports that carry inter-CSI-RS resource feedback, setup of asingle PUCCH feedback mode is preferred. Some examples of suchinter-CSI-RS resource feedback may include a single RI feedback. Forexample, the network may require a single RI report for two or moreCSI-RS resources that feedback is requested for. Such alignment of rankenables a network to perform joint transmission based on per-CSI-RSresource feedback.

Another example of such inter-CSI-RS resource feedback may includeaggregate CQI feedback. Aggregate CQI is the CQI assuming jointtransmission from one or more transmission points. Another example ofsuch inter-CSI-RS resource feedback may include aggregate PMI. AggregatePMI is the PMI assuming joint transmission from one or more transmissionpoints. Another example of such inter-CSI-RS resource feedback mayinclude inter-TP phase feedback. The phase feedback corresponding tophase alignment between two CSI-RS resources for joint transmission.

In various embodiments, feedback modes are defined for two or moreCSI-RS resource joint feedback configuration according to Table 3 below.

TABLE 3 (PMI Feedback Type, CoMP Feedback Type) No PMI, Single No PMI,Single One PMI, One Two CSI- PMI, Two CSI-RS CSI-RS RS CSI-RS ResourceResource Resource resource PUCCH Wideband Mode 1-0 Mode 1-1 Mode 1-4Mode 1-5 CQI (wideband CQI) Feedback UE Selected Mode 2-0 Mode 2-1 Mode2-4 Mode 2-5 Type (subband CQI)

FIG. 6 illustrates feedback reporting corresponding to multiple CSI-RSresources, which may be multiplexed in time in accordance with anexemplary embodiment. In this illustrative embodiment, independentreports are multiplexed (i.e., an independent report type (e.g.,wideband CQI associated with each CSI-RS resource) is configured with asingle set of periodicity/offset parameters across all CSI-RSresources). New report types, like aggregate CQI, are transmitted withthe correspondingly-defined timing parameters (e.g., Nd_(aggregateCQI),Noffset_(aggregateCQI)).

FIG. 7 illustrates feedback reporting for multiple CSI-RS resources,which may be configured together for certain report types in accordancewith an exemplary embodiment. In this illustrative embodiment, reportsfor multiple CSI-RS resources may be configured together for certainreport types, such as wideband/subband CQI or wideband/subband PMI.Further, the CQIs may be jointly encoded with differential encoding. Insuch a case, PUCCH Format 3 may be used for transmission of such newreport type. The inter-CSI-RS resources CQIs, such as an aggregate CQI,are configured separately with their timing parameters (e.g.,Nd_(aggregateCQI), Noffset_(aggregateCQI)). In various embodiments, oneor more of the report types (e.g., aggregate CQI, inter-TP phase) can bemade configurable within a single mode. Such configuration may beindicated by RRC configuration as a submode parameter for that mode.

FIGS. 8A and 8B illustrate examples of a single periodic PUCCHconfigured with UE autonomous TP switching in accordance withillustrative embodiments of the present disclosure. In theseembodiments, the UE may transmit the CSI corresponding to a singleCSI-RS resource only. The choice of which CSI to transmit may beperformed by the UE based on performance (e.g., CQI or RSRP). The UEmeasures the CSI of individual CSI-RS resources and switches between thereporting types based on the best CQI or RSRP. A CSI-RS Resourceindicator (CRI) may be sent separately to indicate switching. FIG. 8Aillustrates an example embodiment where the RI and CRI are separatelysignaled. FIG. 8B illustrates another example embodiment where the RIand CRI are jointly encoded.

Various embodiments of the present disclosure provide indications of CQIreference resource and interference measurement resource. A CSIreference resource is the resource that UE's feedback should correspondto. The UE implementation is not precluded from averaging over “similar”subframes. Interference measurement in Release-10 relies on CRS that areavailable in every subframe. Hence, no reference to interferencemeasurement is made in previous CSI reference resource definitions. 3GPP36.213 section 7.2.3 provides a definition of the CSI referenceresource.

In various embodiments, the network may explicitly indicate the IMresource for periodic CSI configuration. The IM resource (CSI-IMresource) index(s) and CSI-RS resource index(s) are associated with eachPUCCH feedback mode configuration and may be explicitly indicated withRRC configuration for one or more periodic CSI configuration (or CSIprocesses) as illustrated in Table 4 below. As a result, the CSIreference resource definition may be modified to incorporate IM resourcefor periodic CSI reporting.

TABLE 4 Periodic CSI Configuration CSI-RS Resource Index IMR IndexConfiguration X Y

In some embodiments, the reference subframe may be defined withoutreference to the interference measurement. Interference may be based onmeasurements on the subframes with configured IMR resource(s). It isassumed that UE performs interpolation/extrapolation of interference ifthe reference subframe does not include corresponding IMR resource(s).

FIGS. 9A and 9B illustrate examples of a reference subframe withconfiguration of IMR and CSI subframe subsets in accordance with variousembodiments of the present disclosure. In this illustrative embodiment,the downlink transmissions to the UE have at least two differentsubsets, such as with enhanced Intercell Interference Coordination(eICIC), or other transmission modes (e.g., transmission mode 10). Forsuch subframe subsets, the interference measurement is on thecorresponding subframe subset as configured for that CSI request (i.e.,the interference measurement is an element of the CSI subframe setlinked to the periodic CSI report when that UE is configured with CSIsubframe sets). In other words, the configured CSI-LM resource withinthe subframe subset belonging to the CSI reference resource is used toderive the interference measurement.

For example, as illustrated in FIG. 9A, two different types of subframesubsets 905 and 910 are present within the downlink subframes 900transmitted to the UE. Within each of the subframe subsets, the networkconfigures IM resources 915 and 920 within the respective subframesubsets 905 and 910. For feedback reporting in the UCI transmission 925,the UE uses the subframe subset belonging to the CSI reference resourceto derive the interference measurement. As illustrated, for the CSIreference resource (i.e., n_(CQI) _(—) _(ref)) being in subframe subset905 (i.e., in subframe 905 a), the UE uses the IM resource 915 in thesubframe 905 a (which is part of subframe subset 905) to derive theinterference measurement. For example, the UE measures interferenceusing the IM resource 915 to calculate a CQI value or values which arethen reported as feedback in the UCI transmission 925. Even though theIM resource 920 in subframe 910 d may be closer in time or frequency tothe UCI transmission 925, the UE still uses the configured IM resourcewithin the subframe subset belonging to the CSI reference resource toderive the interference measurement.

In another example, as illustrated in FIG. 9B, two different types ofsubframe subsets 955 and 960 are present within the downlink subframes950 transmitted to the UE. Within each of the subframe subsets, thenetwork configures IM resources 965 and 970 within the respectivesubframe subsets 955 and 960. For feedback reporting in the UCItransmission 975, the UE uses the subframe subset belonging to the CSIreference resource to derive the interference measurement. Asillustrated, for the CSI reference resource (i.e., n_(CQI) _(—) _(ref))being in subframe subset 955 (i.e., in subframe 955 b), the UE uses theIM resource 965 in the subframe 955 a (which is part of subframe subset955) to derive the interference measurement. For example, the UEmeasures interference using the IM resource 965 to calculate a CQI valueor values which are then reported as feedback in the UCI transmission975. Even though the IM resource 970 in subframe 960 c may be closer intime or frequency to the UCI transmission 975, the UE still uses theconfigured IM resource within the subframe subset belonging to the CSIreference resource to derive the interference measurement.

Additionally, because the processing of the interference measurement(e.g., receiving the IM resource symbol, measuring interference,calculating a corresponding CQI value or values, etc.) may take time,the UE may actually pass up some configured IM resource that occurscloser in time to the UCI transmission 925 or 975 in order to insureaccurate and timely reporting of the feedback associated with theinterference measurement. The downlink and uplink transmissionsillustrated in FIGS. 9A and 9B may be implemented in a TDD or FDDsystem.

In one illustrative embodiment, with the IM resource configuration, thereference subframe is based on the intersection of the IM resource andthe CSI subframe subset. This can be achieved by further modifying thedefinition of a valid downlink subframe. For example, in the timedomain, the CSI reference resource may be defined by a single downlinksubframe n-n_(CQI) _(—) _(ref), where, for periodic CSI reporting,n_(CQI) _(—) _(ref) is the smallest value greater than or equal to 4,such that it corresponds to a valid downlink subframe. Additionally, adownlink subframe in a serving cell shall be considered to be valid if:the downlink subframe is configured as a downlink subframe for that UE;except for transmission mode 9, the downlink subframe is not an MBSFNsubframe; the downlink subframe does not contain a DwPTS field in casethe length of DwPTS is 7680·T_(s) and less; the downlink subframe doesnot fall within a configured measurement gap for that UE; and forperiodic CSI reporting, it is an element of the CSI subframe set linkedto the periodic CSI report when that UE is configured with CSI subframesets and an element of a subframe set of the interference measurementresource linked to the periodic CSI report if the UE is configured withinterference measurement resources.

With PUSCH based aperiodic feedback modes, higher UCI overhead may besupported than PUCCH based periodic feedback modes, whose capacity islimited by that supported by Format 3 (22 bits). This is suited fortransmission of UCI corresponding to multiple CSI-RS resources in CoMP.Aperiodic feedback modes are captured provided in 3GPP TS 36.213. If nointer-CSI-RS resource feedback is supported, then no new modes need tobe defined for aperiodic CSI. DCI Format 0 (or 4) supports a “CSIrequest field”, which indicates whether aperiodic CSI is turned on andon which cells (e.g., carriers) CSI is to be reported as shown in Table7.2.1-1A of 3GPP TS 36.213.

Similarly, a CSI request may be needed to indicate the set of CSI-RSresources for CoMP. In one exemplary embodiment, an independent CSIrequest field is defined for CoMP according to Table 5 below.

TABLE 5 Value of CSI request field Description ‘00’ No aperiodic CSIreport is triggered ‘01’ Aperiodic CSI report is triggered for CSI-RSresource 1 (or any configured fixed CSI-RS resource or CSIconfiguration) ‘10’ Aperiodic CSI report is triggered for a 1^(st) setof CSI-RS resources (or CSI configurations) configured by higher layers‘11’ Aperiodic CSI report is triggered for a 2^(nd) set of CSI-RSresources (or CSI configurations) configured by higher layers

In another embodiment, a jointly encoded CSI request field may be used.An example with 2-bit encoding is illustrated in Table 6 below. In thisexample, CoMP is only supported on the serving cell. The serving cellmay be replaced by any fixed cell on which CoMP is configured.

TABLE 6 Value of CSI request field Description ‘00’ No aperiodic CSIreport is triggered ‘01’ Aperiodic CSI report is triggered for servingcell c and 1^(st) set of CSI-RS resources (or CSI configurations)configured by higher layers on serving cell c ‘10’ Aperiodic CSI reportis triggered for serving cell c and 2^(nd) set of CSI-RS resources (orCSI configurations) configured by higher layers on serving cell c ‘11’Aperiodic CSI report is triggered for a 1^(st) set of serving cellsconfigured by higher layers (based on a single CSI-RS resource per eachcell that is configured by higher layers)

The set of feedback modes in Table 7.2.1-1A of 3GPP TS 36.213 can bereused, and if more than one CSI-RS resources are configured, the UEaggregates the per-CSI-RS feedback corresponding to the modes configuredon each CSI-RS resource. For example, if mode 1-2 is configured onCSI-RS resource 1 and mode 2-2 on CSI-RS resource 2, the UE aggregatescorresponding CSI.

In other embodiments, some inter-CSI-RS feedback may be supported.Examples of inter-CSI-RS feedback include: aligned RI feedback,aggregate CQI feedback, aggregate PMI, and inter-TP phase feedback.

In one exemplary embodiment, the aperiodic modes are defined for CoMPwith two CSI-RS resources when one or more inter-CSI-RS resourcefeedback modes are supported as illustrated in Table 7 below.

TABLE 7 (PMI Feedback Type, CoMP Feedback Type) Single Multiple SingleMultiple No PMI, PMI, PMI, No PMI, PMI, PMI, Single Single Single TwoCSI- Two CSI- Two CSI- CSI-RS CSI-RS CSI-RS RS RS RS Resource ResourceResource Resource Resource Resource PUSCH Wideband Mode 1-2 Mode 1-5 CQI(wideband Feedback CQI) Type UE Mode 2-0 Mode 2-2 Mode 2-3 Mode 2-5Selected (subband CQI) Higher Mode 3-0 Mode 3-1 Mode 3-3 Mode 3-4 Layer-configured (subband CQI)

The individual mode definitions and methods to support inter-CSI-RSresource feedback are further described below. The CSI configuration isdefined above and may be used interchangeably with CSI-RS resources (ifthey share the same interference measurement resource configuration).

The mode 2-3 is for a UE-selected subband feedback for two CSIconfigurations. In this feedback mode, the UE selects a first set of Mpreferred subbands of size k (where k and M are given in Table 7.2.1-5,36.213 for each system bandwidth range) within the set of subbands S forthe first CSI configuration. The UE selects a second set of M preferredsubbands of size k within the set of subbands S for the second CSIconfiguration. The UE also reports one CQI value reflecting transmissiononly over the first M selected subbands determined in the previous stepfor the first CSI configuration and another CQI value reflectingtransmission only over the second M selected subbands determined in theprevious step for the second CSI configuration. Each CQI representschannel quality for the first codeword of the corresponding CSIconfiguration, even when RI>1. Additionally, the UE reports one widebandCQI value, which is calculated assuming transmission on set S subbandsfor each CSI configuration. The wideband CQI represents channel qualityfor the first codeword of the corresponding CSI configuration, even whenRI>1.

For the same rank, in one example, a single RI is reported for both CSIconfigurations. For transmission mode 3, the reported CQI values arecalculated conditioned on the reported RI. For other transmission modes,the reported CQI values are reported conditioned on rank 1.

For wideband aggregate CQI, in one example, the UE also reports onewideband aggregate CQI value, which is calculated assuming jointtransmission on set S subbands from the two CSI resources. In anotherexample, the aggregate CQI is differentially encoded with the per-CSI-RSwideband CQI.

For a wideband inter-CSI-RS phase, in one example, the UE reports awideband inter-CSI-RS resource phase feedback corresponding to the twoCSI-RS resources of the two CSI configurations.

The mode 3-3 is for higher layer configured subband feedback for two CSIconfigurations. In this feedback mode, a UE reports a wideband CQI valuewhich is calculated assuming transmission on set S subbands per CSIconfiguration. The UE also reports one subband CQI value for each set Ssubband and each CSI configuration. The subband CQI value is calculatedassuming transmission only in the subband. Both the wideband and subbandCQI represent channel quality for the first codeword, even when RI>1.

For the same rank, in one example, a single RI is reported for both CSIconfigurations. For transmission mode 3, the reported CQI values arecalculated conditioned on the reported RI. For other transmission modes,the reported CQI values are reported conditioned on rank 1.

For wideband aggregate CQI, in one example, the UE shall also report onewideband aggregate CQI value, which is calculated assuming jointtransmission on set S subbands from the two CSI resources. In anotherexample, the aggregate CQI is differentially encoded with the per-CSI-RSwideband CQI.

For subband aggregate CQI, in one example, the UE shall also report onesubband aggregate CQI value for each set S subband, which is calculatedassuming joint transmission from the two CSI-RS resources. In anotherexample, the subband aggregate CQI is differentially encoded with thewideband aggregate CQI. The subband differential aggregate CQI offsetlevel is equal to the subband aggregate CQI index minus the widebandaggregate CQI index. A mapping of subband differential aggregate CQIvalue to offset level is provided in Table 8 below.

TABLE 8 Subband differential CQI value Offset level 0 0 1 1 2 ≧2 3 ≦−1

The mode 3-4 is for higher layer configured subband PMI/CQI feedback fortwo CSI configurations. In this feedback mode, a single precoding matrixis selected for each CSI configuration from the codebook subset of thecorresponding CSI configuration assuming transmission on set S subbands.A UE reports one subband CQI value per codeword for each set S subbandand for each CSI configuration which is calculated assuming the use ofthe single precoding matrix corresponding to the CSI configuration inall subbands and assuming transmission in the corresponding subband. AUE reports a wideband CQI value per codeword per CSI configuration,which is calculated assuming the use of the single precoding matrixcorresponding to the CSI configuration in all subbands and transmissionon set S subbands. The UE reports the selected single precoding matrixindicator per CSI configuration except for transmission mode 9 with 8CSI-RS ports configured in which case a first and second precodingmatrix indicator are reported corresponding to the selected singleprecoding matrix per CSI configuration.

For the same rank, in one example, a single RI is reported for both CSIconfigurations. For transmission modes 4, 8, and 9, the reported PMI andCQI values are calculated conditioned on the reported RI. For othertransmission modes, the reported PMI and CQI values are reportedconditioned on rank 1.

For wideband aggregate CQI, in one example, a UE reports a widebandaggregate CQI value per codeword, which is calculated assuming jointtransmission using the single precoding matrix corresponding to each CSIconfiguration in all subbands and transmission on set S subbands.

For subband aggregate CQI, in one example, a UE reports a subbandaggregate CQI value per codeword for each set S subband, which iscalculated assuming joint transmission using the single precoding matrixcorresponding to each CSI configuration in the corresponding subband.

For wideband Inter CSI-RS resource phase, in one example, the UE shallreport a wideband inter-CSI-RS resource phase feedback corresponding tothe two CSI-RS resources corresponding to the CSI configurationsassuming joint transmission on set S subbands.

For wideband aggregate CQI with phase feedback, in one example, a UEshall report a wideband aggregate CQI value per codeword, which iscalculated assuming joint transmission using the single precoding matrixcorresponding to each CSI configuration in all subbands, using thesingle wideband inter-CSI-RS resource phase feedback, and transmissionon set S subbands.

For subband aggregate CQI with phase feedback, in one example, a UEshall report a subband aggregate CQI value per codeword for each set Ssubband, which is calculated assuming joint transmission using thesingle precoding matrix corresponding to each CSI configuration, usingthe single wideband inter-CSI-RS resource phase feedback in thecorresponding subband. In another example, the subband aggregate CQI isdifferentially encoded with the wideband aggregate CQI.

The mode 1-5 is for wideband feedback for two CSI resources. In thisfeedback mode, for each subband, a preferred precoding matrix for eachCSI configuration is selected from the codebook subset of thecorresponding CSI configuration assuming transmission only in thesubband. For each CSI configuration, a UE reports one wideband CQI valueper codeword, which is calculated assuming the use of the correspondingselected precoding matrix in each subband and transmission on set Ssubbands. For each CSI configuration, the UE reports the selectedprecoding matrix indicator for each set S subband except fortransmission mode 9 with 8 CSI-RS ports configured in which case a firstprecoding matrix indicator i₁ is reported for the set S subbands and asecond precoding matrix indicator i₂ is reported for each set S subband.The subband size is defined in Table 7.2.1-3 in 3GPP TS 36.213.

For the same rank, in one example, a single RI is reported for both CSIconfigurations. For transmission modes 4, 8, and 9, the reported PMI andCQI values are calculated conditioned on the reported RI. For othertransmission modes, the reported PMI and CQI values are reportedconditioned on rank 1.

For subband inter-CSI-RS phases, in one example, an inter-CSI-RS phaseis reported per subband for assuming transmission only in the subband.

For wideband aggregate CQI with subband inter-CSI-RS phase, in oneexample, a UE reports one aggregate wideband CQI value per codeword,which is calculated assuming joint transmission and the use of thecorresponding selected precoding matrix in each subband, inter-CSI-RSphase per subband and transmission on set S subbands.

The mode 2-5 is for UE selected subband feedback for two CSIconfigurations and multiple PMI. In this feedback mode, the UE performsjoint selection of the set of M preferred subbands of size k within theset of subbands S and a preferred single precoding matrix selected fromthe codebook subset that is preferred to be used for transmission overthe M selected subbands. The M preferred subbands and the associatedsingle precoding matrix are obtained for each CSI configuration. Foreach CSI configuration, the UE reports one CQI value per codewordreflecting transmission only over the corresponding selected M preferredsubbands and using the same corresponding selected single precodingmatrix in each of the M subbands. Except for transmission mode 9 with 8CSI-RS ports configured, for each CSI configuration, the UE also reportsthe corresponding selected single precoding matrix indicator preferredfor the M selected subbands. For each CSI configuration, a UE alsoreports the corresponding selected single precoding matrix indicator forall set S subbands. For transmission mode 9 with 8 CSI-RS portsconfigured, for each CSI configuration, a UE reports a correspondingfirst precoding matrix indicator for all set S subbands. For each CSIconfiguration, a UE also reports a corresponding second precoding matrixindicator for all set S subbands and another corresponding secondprecoding matrix indicator for the M selected subbands. For each CSIconfiguration, a single precoding matrix is selected from the codebooksubset of the corresponding CSI configuration assuming transmission onset S subbands. For each CSI configuration, a UE reports an associatedwideband CQI value per codeword, which is calculated assuming the use ofthe corresponding single precoding matrix in all subbands andtransmission on set S subbands.

In one example, a single RI is reported for both CSI configurations. Fortransmission modes 4, 8, and 9, the reported PMI and CQI values arecalculated conditioned on the reported RI. For other transmission modes,they are reported conditioned on rank 1.

For wideband aggregate CQI, in one example, a UE reports a widebandaggregate CQI value per codeword, which is calculated assuming jointtransmission using the single precoding matrix corresponding to each CSIconfiguration in all subbands and transmission on set S subbands.

For wideband inter-CSI-RS resource phase, in one example, the UE reportsa wideband inter-CSI-RS resource phase feedback corresponding to the twoCSI-RS resources corresponding to the CSI configurations assuming jointtransmission on set S subbands.

For wideband aggregate CQI with wideband phase, in one example, a UEreports a wideband aggregate CQI value per codeword, which is calculatedassuming joint transmission using the single precoding matrixcorresponding to each CSI configuration in all subbands, using thewideband inter-CSI-RS resource phase feedback, and transmission on set Ssubbands.

For selection of M subbands assuming joint transmission, in one example,the UE performs joint selection assuming joint transmission from two CSIconfigurations of the set of M preferred subbands of size k within theset of subbands S and a preferred single precoding matrix selected fromthe codebook subset for each CSI configuration that is preferred to beused for transmission over the M selected subbands.

For per-CSI-RS resource CQI over the selected M subbands, in oneexample, the UE reports one CQI value per codeword reflecting jointtransmission only over the corresponding selected M preferred subbandsfor joint transmission and using the same corresponding selected singleprecoding matrix for each CSI configuration in each of the M subbandsfrom the previous step.

For inter-CSI-RS phase for selected M subbands, in one example, the UEreports a single inter-CSI-RS resource phase feedback assuming jointtransmission over the selected M preferred subbands for jointtransmission.

For aggregate CQI on selected M subbands, in one example, the UE reportsone aggregate CQI value per codeword reflecting joint transmission onlyover the corresponding selected M preferred subbands for jointtransmission and using the corresponding selected single precodingmatrix for each CSI configuration, and the selected single inter-CSI-RSresource phased feedback, in each of the M subbands.

In one example, the selected single RI for both CSI configurations, asdefined in the above feedback modes, may be based on the CSIconfiguration with the largest wideband CQI. In another example, theselected single RI is based on the CSI configuration with the largestRI. In another example, the RI is based on one of the CSIconfigurations, which may be predefined or configured by higher layersor fixed (e.g., configuration 1).

For aggregate CQI, the assumed IM resource for interference measurementmay be separately configured by higher layers or implicitly defined(e.g., measure all the interference other than the CSI-RS resourcescorresponding to the two CSI configurations).

If both the CSI configurations correspond to the same CSI-RS resourcebut different IMR resources, then some of the inter-CSI-RS resourcefeedback need not be supported. There is no need to report aggregateCQI, inter-CSI-RS phase feedback, or single rank feedback. In oneexample, if there is no need to report this feedback, then these reportsmay be dropped and instead replaced by other reports. For example,multiple rank feedback may be supported or CQI of the individual CSIconfigurations may be encoded differentially. However, if the CSIconfigurations share the same CSI resource, it may not be preferable touse the modes defined above. More generally, in each of the feedbackmodes defined, reports corresponding to more than two CSI configurationscan be supported. Similar definitions for the inter-CSI-RS resourcefeedback may be used with simple extensions of definitions describedherein.

FIG. 10 illustrates a process for CSI feedback reporting by a UE in acoordinated multipoint communication system in accordance with variousembodiments of the present disclosure. For example, the process depictedin FIG. 10 may be performed by the transmitter 405 and/or receiver 410in FIG. 4. The process may also be implemented by the UE 505 in FIG. 5.

The process begins with the UE identifying that downlink transmissionsto the UE are configured with at least two CSI subframe subsets (step1005). For example, in step 1005, the network may use eICIC or configuretransmission mode 10. The UE then identifies an interference measurementresource within one of the CSI subframe subsets belonging to a CSIreference resource (step 1010). For example, in step 1010, the CSIreference resource is a resource corresponding to feedback of the UE.

The UE then uses the identified interference measurement resource toderive an interference measurement (step 1015). For example, in step1015, the UE performs the interference measurement using the IM resourceon the corresponding subframe subset as configured for that CSI request.The UE then transmits CSI feedback information based on the interferencemeasurement (step 1020), with the process terminating thereafter. Forexample, in step 1020, the UE may transmit the CSI feedback informationin a UCI transmission to a base station. The CSI feedback informationmay include one or more CQI values that are computed using the derivedinterference measurement. The CSI feedback by the UE corresponds to aCSI process (or TP) that is associated with the CSI-RS resource and aninterference measurement resource. The CSI process may be configured forthe UE via higher layer signaling.

Although FIG. 10 illustrates an example of a process for CSI feedbackreporting by a UE in a coordinated multipoint communication system,various changes may be made to FIG. 10. For example, while shown as aseries of steps, various steps in each figure could overlap, occur inparallel, occur in a different order, or occur multiple times.

Although the present disclosure has been described with an exemplaryembodiment, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for channel state information (CSI) feedback reporting by a user equipment (UE) in a coordinated multipoint communication system, the method comprising: when downlink transmissions to the UE are configured with at least two CSI subframe subsets, identifying an interference measurement resource within one of the CSI subframe subsets belonging to a CSI reference resource; and using the identified interference measurement resource to derive an interference measurement.
 2. The method of claim 1 further comprising transmitting CSI feedback information based on the interference measurement to a base station in an uplink control information transmission.
 3. The method of claim 2, wherein the CSI reference resource is a resource corresponding to feedback of the UE.
 4. The method of claim 1, wherein CSI feedback by the UE corresponds to a CSI process that is associated with a CSI-RS resource and an interference measurement resource.
 5. The method of claim 4, wherein the CSI process is configured for the UE via higher layer signaling.
 6. The method of claim 1, wherein the UE is configured to report feedback for independent periodic physical uplink control channel (PUCCH) reporting for multiple CSI configurations and wherein periodic feedback mode parameters for two or more CSI configurations are set up independently.
 7. A method for receiving channel state information (CSI) feedback reporting by base station in a coordinated multipoint communication system, the method comprising: receiving, in an uplink control information transmission from a user equipment (UE), CSI feedback based on an interference measurement, wherein downlink transmissions to the UE are configured with at least two CSI subframe subsets, and wherein the interference measurement is derived using an interference measurement resource identified within one of the CSI subframe subsets belonging to a CSI reference resource.
 8. The method of claim 7 further comprising identifying a channel quality information value computed using the interference measurement from the CSI feedback information.
 9. The method of claim 7, wherein the CSI reference resource is a resource corresponding to feedback of the UE.
 10. The method of claim 7, wherein CSI feedback by the UE corresponds to a CSI process that is associated with a CSI-RS resource and an interference measurement resource.
 11. The method of claim 10, wherein the CSI process is configured for the UE via higher layer signaling.
 12. An apparatus in a user equipment (UE) capable of channel state information (CSI) feedback reporting in a coordinated multipoint communication system, the apparatus comprising: a controller configured to: when downlink transmissions to the UE are configured with at least two CSI subframe subsets, identify an interference measurement resource within one of the CSI subframe subsets belonging to a CSI reference resource; and use the identified interference measurement resource to derive an interference measurement.
 13. The apparatus of claim 12 further comprising a transmitter configured to transmit CSI feedback information based on the interference measurement to a base station in an uplink control information transmission.
 14. The apparatus of claim 13, wherein the CSI reference resource is a resource corresponding to feedback of the UE.
 15. The apparatus of claim 12, wherein CSI feedback by the UE corresponds to a CSI process that is associated with a CSI-RS resource and an interference measurement resource.
 16. The apparatus of claim 15, wherein the CSI process is configured for the UE via higher layer signaling.
 17. The apparatus of claim 12, wherein the UE is configured to report feedback for independent periodic physical uplink control channel (PUCCH) reporting for multiple CSI configurations and wherein periodic feedback mode parameters for two or more CSI configurations are set up independently.
 18. An apparatus for receiving channel state information (CSI) feedback reporting by base station in a coordinated multipoint communication system, the apparatus comprising: a receiver configured to receive, in an uplink control information transmission from a user equipment (UE), CSI feedback information based on an interference measurement, wherein downlink transmissions to the UE are configured with at least two CSI subframe subsets, and wherein the interference measurement is derived using an interference measurement resource identified within one of the CSI subframe subsets belonging to a CSI reference resource.
 19. The apparatus of claim 18 further comprising a controller configured to identify a channel quality information value computed using the interference measurement from the CSI feedback information.
 20. The apparatus of claim 18, wherein the CSI reference resource is a resource corresponding to feedback of the UE.
 21. The apparatus of claim 18, wherein CSI feedback by the UE corresponds to a CSI process that is associated with a CSI-RS resource and an interference measurement resource.
 22. The apparatus of claim 21, wherein the CSI process is configured for the UE via higher layer signaling. 